Multi-Carrier Noncontact Signal Detection with Noise Suppression Based on a Phase-Locked Loop

ABSTRACT

A non-contact signal detection system for detecting movement associated with a subject. A carrier source is configured to generate a first carrier signal in phase coherence with a second carrier signal. A phase-locked loop includes noise pre-cancellation system for suppressing the noise associated with a beat signal and a controlled oscillation system. The noise pre-cancellation system can be configured to phase-lock the beat signal to a first reference signal in order to stabilize the phase of the beat signal and pre-cancel the noise associated with the beat signal. The controlled oscillation system can include a propagation pathway on which a transmission signal is phase-modulated with a vibratory signal of the subject. Once acquired, the vibratory signal can have suppressed noise.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 16/060,781filed 8 Jun. 2018, which US Application is a US National Stage Entry ofPCT/US2016/065871 filed on 9 Dec. 2016, which US National Stage Entryclaims the benefit under 35 USC § 119(e) of U.S. Provisional PatentApplication No. 62/265,446 filed 10 Dec. 2015, the entirety of each ofwhich is incorporated herein by reference as if set forth herein in itsentirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

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SEQUENCE LISTING

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STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINTINVENTOR

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BACKGROUND OF THE DISCLOSURE 1. Field of the Invention

Aspects of the present disclosure relate to systems and methods fornon-contact signal detection of movement associated with a subject.

2. Description of Related Art

There has been a growing interest in developing noncontact vital signdetection systems due to their promising applications in the field ofbiomedical monitoring, health care, physical monitoring for astronauts,and search and rescue after mudslides or earthquakes. Various wirelesssolutions have been developed for vital sign detection using thestepped-frequency continuous wave (SFCW), the frequency modulatedcontinuous wave (FMCW), the Doppler radar, and the impulse-basedultrawideband radar. SFCW, FMCW, and impulse-based radar provideflexibility in controlling the frequency band to meet the applicationrequirement on the band and resolution and provide both distance andimage information. However, they pose high requirements on the frequencychirp linearity and bandwidth to accurately detect small displacementsin sub-millimeters and even millimeters. Thus, to realize the detectionof vital signs in millimeters, these solutions place a critical demandon the linearity and bandwidth of detecting waves, which requires acomplex subsystem to achieve. The Continuous Wave (CW) Doppler radaruses the frequency or phase shift in the reflected radar signal todetect physiological movements. It can reach a resolution ofsub-millimeters and is suitable for vital sign detection, includingdetection of the respiration and heartbeat of a subject.

Vital sign detection through Doppler radar is based on phase modulationof the reflected signal at the surface of the human chest. Chestdisplacement due to heartbeat and respiration is exhibited in the phasevariation of microwave signals, and a larger displacement causes a moreobvious phase variation. For instance, for human beings at rest, thechest displacement caused by respiration and heartbeat is typically 4-12mm and 0.2-0.5 mm, respectively. Therefore, the respiration signal has astronger power spectrum density than the heartbeat signal in Dopplerdetection. As the vital sign is contained in the phase of microwavesignals, phase noise of the received signal has a significant influenceon the vital sign detection. For instance, it can raise the backgroundnoise floor, deteriorate the performance of the signal, and impair thesignal-to-noise ratio (SNR), which can decrease the detection accuracyand distance. Residual phase noise, which increases with detectiondistance as well as the oscillator phase noise level, exists in almostall detection environments, while the transmission path noise isassociated with the surroundings and is especially notable inapplications with complex environments, such as search and rescue afterearthquakes.

It is with respect to these and other considerations that the variousaspects of the disclosed technology as described below are presented.

BRIEF SUMMARY OF THE INVENTION

Aspects of the present disclosure relate to systems and methods fornon-contact signal detection of movement associated with a subject.

Some aspects of the present disclosure relate to a non-contact signaldetection system for detecting movement associated with a subject. Insome embodiments, the system can include a carrier source configured togenerate a first carrier signal in phase coherence with a second carriersignal. In some embodiments, to establish phase coherence, the carriersource can be phase-locked to a second reference signal generated by areference oscillator. The system can also include a noisepre-cancellation system for suppressing a phase noise and a path noiseassociated with a beat signal. The noise pre-cancellation system can beconfigured to phase-lock the beat signal to a first reference signal tostabilize the phase of the beat signal. In some embodiments, the firstreference signal can be generated by a low noise reference oscillator.

In some embodiments, the noise pre-cancellation system can comprise aphase-frequency detector, a low-pass filter, and a voltage controlledoscillator (VCO). The phase-frequency detector can be in communicationwith the low-pass filter and a demodulator and configured to receive thebeat signal from the demodulator and the first reference signal. Thephase-frequency detector can discriminate the beat signal with thereference signal and transmit a phase control signal. In someembodiments, the phase-frequency detector and low-pass filter cancontrol the phase of the VCO, such that when the VCO is in communicationwith the phase-frequency detector and low-pass filter it can receive thephase control signal and transmit a noise pre-cancelled signal.

The system can also comprise a controlled oscillation system. The noisepre-cancellation system can be in communication with a controlledoscillation system. In some embodiments, the controlled oscillationsystem can comprise a modulator in communication with the noisepre-cancellation system and the carrier source. The modulator can beconfigured to frequency-modulate the first carrier signal and the secondcarrier signal with the noise pre-cancelled signal and transmit atransmission signal to a propagation pathway. In some embodiments, thetransmission signal can comprise both the frequency-modulated firstcarrier and frequency-modulated second carrier. In some aspects, thepropagation pathway can provide a pathway through which the transmissionsignal is wirelessly transmitted to the subject. In some embodiments,the subject may be moving in some way and generate a vibratory signalassociated with that movement. Through the propagation pathway, thetransmission signal can come in contact with the vibratory signal andthe vibratory signal can phase-modulate the transmission signal tocreate a reflected signal. In some embodiments, the first carrier signaland the second carrier signal can also be phase-modulated by thevibratory signal associated with the subject. Through the propagationpathway, the reflected signal can be received by the demodulator.

In some embodiments, the controlled oscillation system can comprise ademodulator. The demodulator can be in communication with thepropagation pathway, the carrier source, and the noise pre-cancellationsystem. The demodulator can be configured to receive the reflectedsignal from the propagation pathway and the second carrier from thecarrier source and transmit the beat signal to the noisepre-cancellation system. The demodulator can be configured to extract abeat signal from the reflected signal. In some embodiments, thedemodulator can be in communication with a data acquisition deviceconfigured to acquire information associated with the movement of thesubject for data analysis from the beat signal.

In some embodiments, the transmission signal can be transmitted to athird branch in communication with and between the modulator and thedemodulator to provide auxiliary feedback to the demodulator. In someembodiments, the vibratory signal can be associated with a vital sign ofthe subject.

In some embodiments, the present invention is a non-contact signaldetection system comprising a noise pre-cancellation system configuredto transmit a noise pre-cancelled signal, and a controlled oscillationsystem configured to receive a first carrier signal, a second carriersignal, and the noise pre-cancelled signal, the controlled oscillationsystem comprising a modulator configured to frequency-modulate the firstcarrier signal and the second carrier signal with the noisepre-cancelled signal to produce frequency-modulated first and secondcarrier signals and wirelessly transmit a transmission signal comprisingthe frequency-modulated first and second carrier signals, and ademodulator configured to receive the transmission signal, wherein thetransmission signal is phase-modulated with a vibratory signal.

The system can further comprise a carrier source configured to generatethe first and second carrier signals, wherein the carrier source isphase-locked to a first reference signal to establish phase coherencebetween the first carrier signal and the second carrier signal.

The carrier source can be in communication with a first branch includingthe first carrier signal power-combined with the second carrier signal,and a second branch including the second carrier signal.

The first branch can be in communication with the modulator and thesecond branch is in communication with the demodulator.

The system can further comprise a low noise reference oscillatorconfigured to generate the first reference signal.

The noise pre-cancellation system can comprise a phase-frequencydetector, a voltage controlled oscillator (VCO), and a low-pass filter,wherein the phase-frequency detector is configured to receive a beatsignal from the demodulator and a second reference signal and is furtherconfigured to phase-lock the beat signal to the second reference signalto stabilize the phase of the beat signal, and wherein the VCO isconfigured to pre-cancel noise associated with the phase-locked beatsignal to transmit the noise pre-canceled signal.

The transmission signal can be transmitted to a third branch incommunication with and between the modulator and the demodulator toprovide auxiliary feedback to the demodulator.

The demodulator can be configured to extract the beat signal from thesecond carrier signal and transmit the beat signal to thephase-frequency detector of the noise pre-cancellation system.

The demodulator can be in communication with a data acquisition deviceconfigured to acquire information associated with the movement of thesubject from the first carrier signal.

The noise pre-cancellation system can transmit the noise pre-cancelledsignal, The controlled oscillation system can receive the first carriersignal, the second carrier signal, and the noise pre-cancelled signal,the modulator can frequency-modulate the first carrier signal and thesecond carrier signal with the noise pre-cancelled signal to produce thefrequency-modulated first and second carrier signals, the modulator canwirelessly transmit the transmission signal, the demodulator can receivethe transmission signal, the noise pre-cancellation system can comprisea phase-frequency detector, a voltage controlled oscillator (VCO), and alow-pass filter, the phase-frequency detector can be phase-locked to abeat signal to a second reference signal to stabilize the phase of thebeat signal, and the VCO cam be configured to pre-cancel noiseassociated with the phase-locked beat signal and transmits a noisepre-canceled signal to the controlled oscillation system.

The system can further comprise a noise pre-cancellation system incommunication with the oscillation system, wherein the oscillationsystem comprises a modulator in communication with the noisepre-cancellation system and the carrier source and configured tofrequency-modulate the first carrier signal and the second carriersignal with a noise pre-cancelled signal from the noise pre-cancellationsystem and transmit the first and second carrier signals to the subject.

The receiver can comprise a demodulator in communication with thecarrier signal, the demodulator configured to frequency demodulate thefirst and second carrier signals.

The demodulator can be further configured to extract a beat signal fromthe second carrier signal and transmit the beat signal to the noisepre-cancellation system.

56. (withdrawn) The non-contact signal detection system of claim 55,wherein the demodulator is in communication with a data acquisitiondevice configured to extract the vibratory signal from the first carriersignal.

Embodiments of the present disclosure can also include a dual-carriersource configured to generate a first carrier signal in phase coherencewith a second carrier signal and a phase-locked loop in communicationwith the dual-carrier source. The phase-locked loop can comprise aphase-frequency detector, a low-pass filter, and a VCO. Thephase-frequency detector can be configured to phase-lock a beat signalto a first reference signal and transmit a phase control signal.Additionally, the VCO can be configured to receive the phase controlsignal, suppress the noise associated with the beat signal, and transmita noise pre-cancelled signal. The noise pre-cancelled signal can then bereceived by the controlled oscillation system, as described previously.

Embodiments of the present disclosure can include a method for detectingmovement associated with a subject. The method can comprise generating,by a carrier source, a first carrier signal in phase coherence with asecond carrier signal. In some embodiments, the generating, by thecarrier source, can comprise phase-locking the first carrier signal andthe second carrier signal with a second reference signal generated by areference oscillator. The method can also include using a noisepre-cancellation system for suppressing a phase noise and a path noiseof a beat signal by phase-locking the beat signal to a first referencesignal to stabilize the phase of the beat signal. Additionally, thenoise pre-cancellation system can be used for transmitting the noisepre-cancelled signal. The method can also comprise using a modulator incommunication with the noise pre-cancellation system and the carriersource for frequency-modulating the first carrier signal and the secondcarrier signal with the noise pre-cancelled signal. Then, the modulatorcan transmit a transmission signal. The transmission signal from thedemodulator can be transmitted to the subject through a propagationpathway. From the propagation pathway, a reflected signal can bereceived, wherein the reflected signal includes the transmission signalphase-modulated with a vibratory signal associated with movement of thesubject. The reflected signal and the second carrier signal can bereceived by a demodulator in communication with the carrier source andthe noise pre-cancellation system, and the beat signal can betransmitted to the noise pre-cancellation system.

In some embodiments, when suppressing the phase noise and the path noiseof the beat signal by phase-locking the beat signal to a first referencesignal to stabilize the phase of the beat signal, the phase frequencydetector can receive the beat signal and the first reference signal andtransmit a phase control signal. The VCO may then receive the phasecontrol signal from the phase frequency detector and pre-cancel thenoise associated with the beat signal.

In some embodiments, the method can also comprise extracting, from thereflected signal, i) information associated with the vibratory signal ofthe subject, and ii) the beat signal, and the extracting can beperformed by the demodulator. In one embodiment, the vibratory signalcan be associated with a vital sign of the subject.

In one embodiment, the method can comprise providing auxiliary feedbackto the demodulator by transmitting the transmission signal to a thirdbranch, the third branch in communication with and between the modulatorand the demodulator.

Embodiments of the present disclosure can also comprise anon-contactsignal detection method. The method can include generating a firstcarrier signal in phase coherence with a second carrier signal;providing a beat signal. The method can include phase-locking the beatsignal to a first reference signal to stabilize the phase of the beatsignal. Then, the method an include suppressing a phase noise and a pathnoise of the beat signal to produce a noise pre-cancelled signal. Usingthe noise pre-cancelled signal, the method can includefrequency-modulating the first carrier signal and the second carriersignal with the noise pre-cancelled signal to produce a transmissionsignal. Then the transmitted signal can be wirelessly transmitted to thesubject through a propagation pathway. Through the propagation pathway,the transmission signal can be phase-modulated with a vibratory signalassociated with the movement of the subject, to produce a reflectedsignal. Then, the reflected signal can be received. Following, themethod can include extracting, from the reflected signal, i) informationassociated with the vibratory signal of the subject, and ii) the beatsignal.

Other aspects and features according to the example embodiments of thedisclosed technology will become apparent to those of ordinary skill inthe art, upon reviewing the following detailed description inconjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying Figures, which are incorporated in and constitute apart of this specification, illustrate several aspects described below.

FIG. 1a illustrates a non-contact signal detection system, in accordancewith one embodiment of the present disclosure.

FIG. 1b illustrates a noise pre-cancellation system, in accordance withone embodiment of the present disclosure.

FIG. 2 illustrates a dual-carrier, non-contact signal detection system,in accordance with one embodiment of the present disclosure.

FIGS. 3a and 3b is a graphical representation of the normalized powermeasured for phase-locked microwave signals as a function of thefrequency offset, in accordance with one embodiment of the presentdisclosure.

FIG. 4 is a linear frequency domain model relating to an embodiment of anon-contact signal detection system, in accordance with one embodimentof the present disclosure.

FIG. 5 is a graphical representation of the measured phase noisespectrum of the beat signal and the reference signal when unlocked andlocked, in accordance with one embodiment of the present disclosure.

FIG. 6 is a schematic of a prior art, direct vital sign detection havinga transmitter antenna and a receiver antenna in communication with a PNANetwork Analyzer.

FIGS. 7a and 7b are graphical representations comparing detection ofvital sign signals with a direct signal (black line) and an unlockedsystem (gray line).

FIGS. 8a and 8b are graphical representations comparing detection ofvital sign signals with a locked system (black line) and an unlockedsystem (gray line), in accordance with one embodiment of the presentdisclosure.

FIGS. 9a-9e are graphical representations comparing detection of vitalsign signals with a locked system and an unlocked system at variousdistances away from a subject, including 100 cm (FIG. 9a ), 150 cm (FIG.9b ), 200 cm (FIG. 9c ), 250 cm (FIG. 9d ), and 300 cm (FIG. 9e ), inaccordance with one embodiment of the present disclosure.

FIGS. 10a-10d illustrate detection of vital sign signals at fourorientations of the subject, including facing front (FIG. 10a ), facingback (FIG. 10b ), facing left (FIG. 10c ), and facing right (FIG. 10d ),in accordance with embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Although preferred exemplary embodiments of the disclosure are explainedin detail, it is to be understood that other exemplary embodiments arecontemplated. Accordingly, it is not intended that the disclosure islimited in its scope to the details of construction and arrangement ofcomponents set forth in the following description or illustrated in thedrawings. The disclosure is capable of other exemplary embodiments andof being practiced or carried out in various ways. Also, in describingthe preferred exemplary embodiments, specific terminology will beresorted to for the sake of clarity.

As used in the specification and the appended claims, the singular forms“a,” “an” and “the” include plural referents unless the context clearlydictates otherwise.

Also, in describing the preferred exemplary embodiments, terminologywill be resorted to for the sake of clarity. It is intended that eachterm contemplates its broadest meaning as understood by those skilled inthe art and includes all technical equivalents which operate in asimilar manner to accomplish a similar purpose.

Ranges can be expressed herein as from “about” or “approximately” oneparticular value and/or to “about” or “approximately” another particularvalue. When such a range is expressed, another exemplary embodimentincludes from the one particular value and/or to the other particularvalue.

Using “comprising” or “including” or like terms means that at least thenamed compound, element, particle, or method step is present in thecomposition or article or method, but does not exclude the presence ofother compounds, materials, particles, method steps, even if the othersuch compounds, material, particles, method steps have the same functionas what is named.

Mention of one or more method steps does not preclude the presence ofadditional method steps or intervening method steps between those stepsexpressly identified. Similarly, it is also to be understood that themention of one or more components in a device or system does notpreclude the presence of additional components or intervening componentsbetween those components expressly identified.

Embodiments of the present disclosure can comprise a non-contact signaldetection system that can suppress the residual phase noise andtransmission path noise, associated with a signal. Carrier waves can betransmitted to a subject and phase-modulated by a vibratory signalassociated with movement of the subject, received, and analyzed. As thereflected signal is transmitted along this path, the signal may beparticularly susceptible to broadband waves due to environmental factorsthat can increase the path noise and phase noise associated with thesignal. This increase in noise can make it particularly challenging toextract a meaningful signal. Embodiments of the present disclosure canreduce the effects of phase and path noise by incorporating amulti-carrier system and a phase-locked loop for pre-canceling noise andthereby improving the quality of vibratory signal detection. Forinstance, in some embodiments using a phase-locked loop design, thesystem can automatically adjust the transmitted signals to suppress thisnoise even when the noise changes during signal detection. Byincorporating a phase-locked loop design, a beat signal can bephase-locked to a reference signal provided by a low-noise oscillatorand the phase-locked loop can control the phase of a voltage controlledoscillator (VCO). Thus, the residual phase noise and path noise can bepre-cancelled and the vital sign signal can be recovered with relativelylow noise.

FIG. 1a illustrates a non-contact signal detection system 100 fordetecting movement associated with a subject 160, in accordance with anembodiment of the presently disclosed technology. As shown, thenon-contact signal detection system 100 comprises a carrier source 110configured to generate a first carrier signal 103 and a second carriersignal 105. The first carrier signal 103 can comprise asignal-extraction carrier, and the second carrier signal 105 cancomprise a noise-suppression carrier. The signal-extraction carrier caninclude a carrier from which a vibratory signal 165 from a subject 160is carried and extracted. The noise-suppression carrier can include acarrier transmitted to a phase-locked loop 120 and from which noise isextracted and suppressed when the noise-suppression carrier proceedsthrough the phase-locked loop. The signal-extraction carrier and thenoise-suppression carrier can be defined by a first signal at a firstfrequency (f1) and a second signal at a second frequency (f2),respectively. Additionally, the signal-extraction carrier and thenoise-suppression carrier may be in phase coherence. As understood bythose skilled in the art, phase coherence can mean the noise-suppressioncarrier and the signal-extraction carrier have a constant phasedifference. As such, the two carriers in phase coherence can propagatethrough the same path during detection, be influenced by the same levelof phase noise, and their phase noises can be pre-cancelled at the sametime by a single pre-canceling signal. In some embodiments, phasecoherence can be established by phase-locking the carrier source 110 toa reference signal 115 or another appropriate reference signal.

As shown, the disclosed non-contact, signal detection system 100comprises a phase-locked loop 120. The phase-locked loop 120 is incommunication with the carrier source 110 through a first branch 113 anda second branch 117 and the reference signal 115. The first branch 113can comprise the first carrier signal 103 (i.e., the signal-extractioncarrier) power-combined with the second carrier signal 105 (i.e., thenoise-suppression carrier). The second branch 117 can comprise thesecond carrier signal 105.

The phase-locked loop 120 can comprise a noise pre-cancellation system130 and a controlled oscillation system. The noise pre-cancellationsystem 130 can be configured to receive a reference signal 115 and abeat signal 135 and lock the beat signal 135 to the reference signal115. The beat signal 135 can comprise the noise-suppression carriermodulated by the vibratory signal of the subject and frequencydemodulated at the demodulator. In other words, the beat signal 135 canbe transmitted by the demodulator 150. In some embodiments, thereference signal 115 can be generated by a high-quality, low-noisereference oscillator. The reference oscillator may comprise anycommercially available, high-quality oscillator, for instance, atemperature-controlled oscillator or a Rubidium clock. As illustrated,in some embodiments, the reference signal 115 in communication with thenoise pre-cancellation system 130 can be the same reference signal 115as that in communication with the carrier source 110.

The noise pre-cancellation system 130 can be configured to cancel thenoise associated with the beat signal 135, such that the beat signal 135has a low phase noise (such as residual phase noise) and a low pathnoise. For instance, in some embodiments, as illustrated at FIG. 1b ,the noise pre-cancelling component can comprise a voltage controlledoscillator (VCO) 137. The VCO 137 can cancel the noise associated withthe beat signal 135, such that the beat signal 135 contains noinformation about the subject's vibratory signal 165 and yet the beatsignal 135 demonstrates a low phase noise and low path noise. Therefore,the VCO 137 can be configured to generate a noise pre-cancelled signalthat can be introduced to the controlled oscillation system.

The controlled oscillation system can comprise a modulator 140, apropagation pathway 145, and a demodulator 150. The modulator 140 can bein communication with the noise pre-cancellation system 130 and a firstbranch 113. Specifically, the modulator 140 can be in communication withthe VCO 137 of the noise pre-cancellation system 130, as illustrated atFIG. 1b . As discussed previously, the first branch 113 can comprise thefirst carrier 103 power-combined with the second carrier 105. Thus, themodulator 140 can be configured to receive the noise pre-cancelledsignal 139 from the noise pre-cancelling component 130, the firstcarrier signal 103, and the second carrier signal 105. Additionally, themodulator can be configured to frequency-modulate the first carriersignal 103 and the second carrier signal 105 with the noisepre-cancelled signal 139.

The modulator 140 can be configured to output the transmission signal143 a, which can be transmitted to the propagation pathway 145. Thetransmission signal 143 a can be considered the result of the frequencymodulation of the first carrier signal 103 (f1′) and the second carriersignal 105 (f2′) with the noise pre-cancelled signal 139. Thepropagation pathway 145 can be a transmission pathway through which thetransmission signal 143 a is wirelessly transmitted to the subject 160.Once the transmission signal 143 a comes in contact with a surface ofthe subject 160, the transmission signal 143 a can be phase-modulatedwith a vibratory signal 165 associated with a movement of the subject160. The product of this phase modulation is that a reflected signal 143b contains within its phase, information about the vibratory signal 165.The reflected signal 143 b can therefore comprise the transmissionsignal 143 a phase-modulated with the vibratory signal 165 of thesubject 160 and can be received by the demodulator 150 of the controlledoscillation system.

The demodulator 150 can be configured to receive the reflected signal143 b from the propagation pathway 145. The reflected signal 143 b canbe carried by both the first carrier signal 103 and the second carriersignal 105, each carrier signal having been frequency-modulated (f1′ andf2′) with the noise pre-cancelled signal 139 by the modulator 140phase-modulated by the vibratory signal 165 of the subject 160 (f1″ andf2″). The demodulator can also be in communication with a second branch117 that is coupled with the carrier source 110 and includes only thesecond carrier signal 105. The demodulator 150 can demodulate the firstcarrier signal 103, extract the vibratory signal information, andtransmit it to the data acquisition device (DAQ) 170. The DAQ 170 canreceive the information about the vibratory signal 165 and can beconfigured to provide information corresponding to the vibratory signal165. Additionally, the demodulator 150 can be in communication with thenoise pre-cancellation system 130 and transmit the beat signal 135carried by the second carrier signal 105 to the noise pre-cancellationsystem 130 to lock the loop 120.

Having a carrier source 110 with two or more carriers can beadvantageous as it allows for effective long-distance detection as wellas noise-suppression without also suppressing the detected vibratorysignal 165. Without a carrier source generating two or more carriers, aphase-locked loop would result in suppression of the vibratory signal aswell as the noise associated with it. As will be understood, the secondcarrier signal 105 can travel through the propagation pathway 145 andthe phase-locked loop 120 while the first carrier signal 103 will onlytravel through the propagation path 145. The beat signal 135 received bythe noise pre-cancellation device 130 can then be noise-suppressedindependent of any information related to the vibratory signal 165,which can be concurrently received at the DAQ 170. The vibratory signal165 received by the DAQ 170 may be further processed for extractingadditional information or parameters associated with the vibratorysignal. When the beat signal 135 is transmitted through the noisepre-cancellation system 130, the vibratory signal information can betreated as path noise and suppressed as well.

While the above-described non-contact signal detection system isdescribed as having two carriers, it is understood that the non-contactsignal detection system can comprise more than two carriers.Additionally, the first and second frequencies of the first carrier andthe second carrier can be adjusted as desired. In some embodiments, thefrequencies of the two carriers can be on a microwave frequency scale,having a frequency anywhere between 300 MHz and 300 GHz. In otherembodiments, the frequencies of the two carriers can be on a radiofrequency scale, having a frequency anywhere between 3 Hz to 300 GHz. Aswill be understood, the frequency of the carrier signals can beincreased, according to different applications. Additionally, in someembodiments, phase-coherence can be established between thesignal-extraction carrier and the noise-suppression carrier. Asdiscussed above, phase coherence can be established by phase-locking thefirst carrier signal 103 and the second carrier signal 105 to areference signal 115. In some embodiments, the reference signal can bethe same reference signal 115 locked to the phase-locked loop 120, asillustrated at FIG. 1, and in other embodiments, the reference signalmay be a low-quality oscillator. As will be understood by those skilledin the art, the carrier signals 103 and 105 need not be locked to ahigh-quality reference signal as the residual phase noise will besuppressed in the phase-locked loop 120.

An exemplary and non-limiting embodiment of the noise pre-cancellationsystem 130 is illustrated at FIG. 1b . The noise pre-cancellation system130 may comprise a phase-frequency detector 131, a low-pass filter 133,and the VCO 137. In some embodiments, the phase-frequency detector 131can be configured to receive the reference signal 115 and the beatsignal 135. The phase-frequency detector 131 can be configured to lockthe beat signal 135 to the reference signal 115. The phase frequencydetector 131 can be in communication with the low-pass filter 133, whichcan in turn be in communication with the VCO 137. In some embodiments,the noise pre-cancellation system 130 can instead comprise a phasedetector or phase comparator.

In some embodiments, the transmission signal 143 a can be transferred tothe subject 160 via a TX antenna 147 and the phase-modulated carriersignal can be received by an RX antenna 149. As used herein, a “subject”may be any applicable living or non-living subject. Alternatively, thesubject may be living and be a human, an animal, a plant, or otherorganism. For instance, the subject may be non-living and created byman, such as a bridge, building, or other structure, or is a non-livingproduct of nature. In some embodiments, the subject 160 may be a livingsubject. For instance, the subject 160 may be a human being and thevibratory signal 165 may comprise information associated with a vitalsign, such as a heartbeat or respiration of the subject. Thedisplacement of a subject's chest, for instance, can create alow-frequency signal that can modulate the transmission signal, suchthat the transmission signal will carry the vital sign information inits phase. Therefore, the vital sign information may be extracted at thedemodulator 150 and received by the DAQ 170. While embodiments of thepresent disclosure may be described in terms of a non-contact, signaldetection system associated with vibratory signals of a living subject,it will be appreciated that embodiments of the present disclosure may beused to detect other vibratory signals. For instance, the device may beapplicable to detecting vibratory signals in structures, such as bridgesor buildings.

Embodiments of the non-contact signal detection system can be used todetect vibratory signals from a subject at a variety of distances. Forinstance, in one embodiment, a non-contact signal detection system canbe used for measuring a vibratory signal of a subject at distancesincluding 50 cm, 100 cm, 150 cm, 150 cm, 200 cm, 250 cm, and 300 cm,without adjusting the power of the system. In embodiments where thedistance is increased, the phase-locked loop 120 may comprise anadditional feedback signal, as illustrated at FIG. 2, providing anadequate power to lock the loop. For instance, in an embodiment, thefeedback signal can be power combined with the received signal, whichthe demodulator can receive as an input. In alternative embodiments, themeasurement distance may be further increased by adjusting the power,the carrier frequencies, the antenna design, and/or other appropriatecomponents and/or parameters of the system.

Additionally, in some embodiments the demodulator 150 can be an I/Qdemodulator. An I/Q demodulator can be advantageous because it canacquire a signal independent of where the subject is located. Forinstance, the I/Q demodulator can cancel a null point associated withthe signal detection. As will be understood, a null point in signaldetection will inhibit signal detection of a subject at particularpositions. I/Q demodulators can be advantageous as they can cancel thenull point by phase-shifting the detected signal by 90 degrees, allowingfor detection of a subject at any position with respect to the dataacquisition device.

As will be understood, embodiments of the present disclosure can includevarious other electrical components for otherwise adjusting the system,including one or more amplifiers, one or more low-pass filters, and/orone or more bandwidth filters.

Example Implementations and Results

Various aspects of the disclosed technology may be still more fullyunderstood from the following description of example implementations andcorresponding results and the images of FIGS. 3-10 d. Some experimentaldata are presented herein for purposes of illustration and should not beconstrued as limiting the scope of the disclosed technology in any wayor excluding any alternative or additional embodiments.

Noise Suppression Design Scheme

The efficacy of a described non-contact signal detection system wastested by incorporating one or more aspects of the present disclosure ina non-contact vital sign detection system 200 comprising a dual-carriersource, a phase-locked loop, and an auxiliary feedback pathway, asillustrated at FIG. 2.

Vital sign detection using CW Doppler radar can involve transmitting amicrowave signal, which is then phase-modulated by the chest surfacedisplacement, and then receiving and demodulating the reflected signalto obtain vital sign information. In the detection process, residualphase noise and path noise may contaminate the received wave, reducingthe quality of the phase information. The residual phase noise, whichmay be due to the deterioration of phase coherence between the receivedand local waves, can affect the beat signal, so it can be considered asthe phase noise of the reflected signal for convenience of analysis. Asthe vital sign information can be contained in the phase of thereflected signal, phase noise should be suppressed to extract alow-noise vital sign signal. Considering the reflected signal as a freerunning VCO that has a high phase noise level, the reflected signal canbe phase-locked to a low-noise, highly stable reference signal. Noisewithin the loop bandwidth can be suppressed, as the phase-locked loopcan be a high-pass filter to the free running VCO. Since the vital signsignal is also within the loop bandwidth, the phase-locked loop willsuppress the desired vital sign signal as well as the noise if a singlecarrier is used. To extract the vital sign signal and reduce the noiseat the same time, a dual-carrier scheme can be used.

Embodiments of the present disclosure can comprise a non-contact vitalsign detection system 200 comprising a dual-carrier source 210 that canreduce the phase noise, as shown in FIG. 2. The non-contact vital signdetection system 200 can comprise microwave signal sources, poweramplifiers, frequency converters, antennas, a phase frequencydiscriminator, a low-pass filter, and a VCO. A microwave signalgenerator 203 (HP 83622B) and PNA network analyzer 205 (Agilent N5222A)can be phase-locked to a 10-MHz reference signal (215) generated by a 10MHz reference oscillator and generate 5.60- and 5.68-GHz microwavesignals, respectively, and as shown. These two carrier signals can thenbe power-combined at 213 and directed to the LO port of an I/Q frequencyupconverter 240 (Hittite HMC925LC5), with the intermediate frequency(IF) signal provided by an 80-MHz VCO (237). The I/Q frequencyupconverter 240 can frequency modulate the two carrier signals with theIF signal. After the frequency of the carrier signals is unconverted by80 MHz, each carrier signal can be amplified and split into twobranches. One branch can be in communication with the TX antenna 247 andprovide the frequency-modulated carrier signals 243 a to the TX antenna247. The TX antenna 247 can then wirelessly transmit thefrequency-modulated carrier signals 243 a to the propagation pathwayover which the carrier signals 243 a are modulated by the vital signsignal 260, to produce a reflected signal 243 b. Then, the reflectedsignals 243 b can be received by the RX antenna 249. The other branchcan provide an auxiliary feedback path 241 to the phase-locked loop toensure stability is achieved during vital sign detection. The auxiliaryfeedback path 241 can ensure that the minimum power is achieved to lockthe loop. For instance, in an embodiment, the auxiliary feedback pathcan provide a power level of around −18 dBm, which, in this instance, isthe minimum power required to lock the loop when there is no RX receivedsignal.

The reflected signals 243 b from the propagation pathway can bepower-amplified and received at a frequency down-converter 250 alongwith the transmission signal from the auxiliary feedback path and thelocal 5.68-GHz microwave signal, generated by the PNA Network Analyzer205. The frequency down-converter 250 can mix these signals andfrequency downconvert them to an 80-MHz beat signal 235 and lowfrequency signals, as well as their noise, including residual phasenoise and path noise.

The phase-locked loop can then lock the 80-MHz beat signal 235 to the10-MHz reference signal 215, and the phase-locked loop can control theVCO's (237) phase to stabilize the phase of the 80-MHz beat signal 235.This means the VCO (237) can pre-cancel the residual phase noise andpath noise in the transmitted carriers so that the 80-MHz beat signal235 and its corresponding received 5.76-GHz carrier have a low phasenoise but contain approximately no vital sign information, which can beconsidered path noise. This system can then provide a clean transmissionpath for the frequency-modulated, 5.60-GHz carrier (upconverted to5.68-GHZ). The demodulation of the 5.68-GHz upconverted signal with the5.68-GHz local signal can provide a low-noise vital sign signal that canbe acquired and analyzed to extract relevant information about thedetected vibratory signal.

Time Domain Mathematical Analysis

The microwave signals from the microwave signal generator and PNAnetwork analyzer can be expressed as:

v ₁(t)=sin(2πf _(a) t+ϕ _(a))+sin(2πf _(b) t+ϕ _(b))  (1)

where f_(a) and f_(b) are 5.68- and 5.60-GHz, respectively, while co,and cob are the corresponding phases of the two signals, respectively.The two signals can be amplified and adjusted to have the about the samepower at the LO port of the frequency upconverter. FIG. 3a is agraphical representation of the normalized power associated with the5.68- and 5.60-GHz signals as a function of the frequency offset.

Then the microwave signals can be mixed with the 80-MHz VCO signal tooutput the frequency upconverted signals at the RF port of the frequencyupconverter. The frequency upconverted signals can be expressed as:

v ₁(t)=sin[2π(f _(a) +f _(v))t+(ϕ_(a)ϕ_(v))] sin[2π(f _(b) +f_(v))t+(ϕ_(b)+ϕ_(v))]  (2)

where f_(v) is 80-MHz and coy represents the phase of the VCO. Afterbeing amplified, the upconverted signals can be transmitted through theTX antenna. The spectrum of the frequency upconverted signals isillustrated in the graphical representation at FIG. 3b . Due to theproperties of the VCO and the frequency upconverter, there may beunwanted sidebands around the desired 5.76- and 5.68-GHz. Thesesidebands can spread in a span of about 2.5-GHz, with a space of 80-MHz.By adjusting the power level and delay/phase at the LO and IF ports ofthe frequency upconverter, the ratio between the carrier and theunwanted sidebands can reach 12-dB. When mixed with a 5.68-GHz localsignal in the frequency downconverter (Hittite HMC951LP4E), both 5.76-and 5.60-GHz signals can produce the 80-MHz beat signal, which can befed back to lock the loop. Thus the 5.60-GHz sideband component caninfluence the system performance, but the −20-dB ratio to 5.76-GHzsignal may significantly reduce such an effect. The higher ordersidebands have little influence on the performance of the system, as thebandpass filter will filter out their corresponding beat signals. Thus,the sidebands can be neglected for the purpose of the followinganalysis, with focus only on the 5.68- and 5.76-GHz signals.

After being transmitted from the TX antenna, the microwave signals canbe phase-modulated by the vital sign signal, including the heartbeat andrespiration. Assuming the displacement of the human chest is x(t), itwill contribute to a delay of τ_(x)=2 x(t)/c or a phase ofφ=2πfτ_(x)=4πx(t)/λ, where c is the speed of electromagnetic wave and λis the wavelength. Thus, the vital sign signal can be detected throughanalyzing the phase of received microwave signals.

The microwave signals received by the RX antenna contain a vital signsignal as well as noise associated with that signal:

v ₃(t)=cos[2π(f _(a) +f _(v))(t+τ)+(ϕ_(a)+ϕ_(v)+ϕ_(n))]+cos[2π(f _(b) +f_(v))(t+τ)(ϕ_(b)+ϕ_(v)+ϕ_(n))]  (3)

where φ_(n)=φ_(pa)+φ_(rd), φ_(pa) and φ_(rd) represent the path noiseand residual phase noise, respectively, and τ=τ_(x)+τ₀ with τ₀=2d₀/c isascribed to the average distance do between the chest and the antenna.The reflected signals may have a low power level, so a low-noise poweramplifier (Hittite HMC902LP3) can be incorporated to adjust the powerlevel of the reflected signals. After amplification, the receivedsignals can be combined with the auxiliary path signals. The auxiliarypath signals may help to improve the locking performance of the system,especially when the amplified received signals are a little lower than−18 dBm, which is required to produce a −10-dBm minimum feedback signalfor the phase-frequency detector.

The effect of the auxiliary path on the extraction of vital sign signalscan be analyzed as follows. To analyze the effect of auxiliary path onthe noise performance of the vital sign signal, the amplitude ratiobetween the auxiliary path and the received signal can be assumed to beα. Thus, the IF port of frequency downconverter is:

$\begin{matrix}{{v_{4} = {{{\sin\;\left( \Theta_{a} \right)} + {\sin\;\left( \Theta_{b} \right)} + {\alpha\;{\sin\left( v_{a} \right)}} + {a\;{\sin\left( v_{b} \right)}}} = {{\sin\left( \Theta_{a} \right)} + {a\;\sin\;\left( v_{\alpha} \right)} + {\alpha\;\sin\;\left( \Theta_{b} \right)} + {a\;{\sin\left( v_{b} \right)}}}}}{where}} & (4) \\{\mspace{79mu}{{\theta_{a} = {{\omega_{v}t} + {\left( {\omega_{a} + \omega_{v}} \right)\tau} + \varphi_{v} + \varphi_{n}}},}} & \left( {4a} \right) \\{\mspace{79mu}{{\theta_{b} = {{\left( {\omega_{b} - \omega_{a} + \omega_{v}} \right)t} + {\left( {\omega_{b} + \omega_{v}} \right)\tau} + \left( {\varphi_{b} - \varphi_{a} + \varphi_{v} + \varphi_{n}} \right)}}\ ,}} & \left( {4b} \right) \\{\mspace{79mu}{{v_{a} = {{\omega_{v}t} + {\left( {\omega_{a} + \omega_{v}} \right)\overset{\hat{}}{\tau}} + \varphi_{v} + {\hat{\varphi}}_{n}}},}} & \left( {4c} \right) \\{\mspace{79mu}{v_{b} = {{\left( {\omega_{b} - \omega_{a} + \omega_{\nu}} \right)t} + {\left( {\omega_{b} + \omega_{v}} \right)\overset{\hat{}}{\tau}} + \left( {\varphi_{b} - \varphi_{a} + \varphi_{\nu} + {\overset{\hat{}}{\varphi}}_{n}} \right)}}} & \left( {4d} \right)\end{matrix}$

Here, v_(a) and v_(b) are the phases of carriers a and b in theauxiliary path. {circumflex over (τ)} and {circumflex over (φ)}_(n)represent the delay and noise introduced by the auxiliary path.

Through the mathematical transform, v₆(t) can be rewritten as:

v ₆=(1+α)sin(x _(a))cos(y _(a))+(1−α)cos x _(a) sin y _(a)  (5)

where x_(a)=(θ_(a)+v_(a))/2 and y_(a)=(θ_(a)−v_(a))/2.

In the short distance (α<<1), 1+a≈1−α. Thus v₆(t) will bev₆=sin(x_(a)+y_(a))=sin(θ_(a)), which implies that the auxiliary pathdoes not influence the vital sign detection. If the ratio α isincreasing to 1, v₆=2 sin(x_(a)) cos(y_(a)). The cosine term is the slowamplitude fluctuation, and the amplitude noise of the controlledoscillation system can be ignored in the phase-locked loop. v₆ is lockedto the reference signal v₅, so ϕ₆=x_(a)=8(ω_(ref)t+φ_(ref)), thus

$\begin{matrix}{v_{7} = {2{\sin\left\lbrack {{8\phi_{ref}} + {\frac{w_{b} - w_{a}}{2}\left( {\tau + \overset{\hat{}}{\tau}} \right)} + \phi_{b} - \phi_{a}} \right\rbrack}}} & (6)\end{matrix}$

where {circumflex over (τ)} is the delay introduced by the auxiliarypath, and it is much smaller than τ. When the ratio is around 1, theeffect of the auxiliary path can be neglected. So the vital sign signalis not degraded in the short distance.

As the detection distance extends, the effect of the auxiliary path onthe vital sign will become apparent. In the long distance (α>>1), v₆=αsin(x_(a)−y_(a))=sin(θ_(a)), the loop is totally locked through theauxiliary path. Without the auxiliary feedback path, he system may havedifficulty with detecting the vital sign signal.

If the auxiliary path is at a lower power, it typically can performbetter. However, it should demonstrate enough power to provide a −10 dBmof v₆, required by the datasheet of phase-frequency detector used in thedescribed systems. In some embodiments, to achieve a −10 dBm of v₆, theauxiliary feedback path should be about −18 dBm, which is the minimumpower required to lock the loop when there is no RX received signal. Theauxiliary path can then provide a stable detection when the amplifiedreflected signal is even lower than −18 dBm.

In embodiments where the amplified received signal is over −18 dBm, theauxiliary path is optional. Then the combined microwave signals can bemixed with a 5.68-GHz local signal split from the PNA network analyzer,producing beat signals at the frequency downconverter IF port:

v ₄(t)=sin[2π(f _(v) t+2π(f _(a) +f _(v))τ+ϕ_(v)+φ_(n)]+sin[2π(f _(b) −f_(a) +f _(v))t+2π(f _(b) +f _(v))τ]+(ϕ_(b)−ϕ_(a)+ϕ_(v)+ϕ_(n))]  (7)

where f_(b)−f_(a)+f_(v) equals 0. The beat signals can be split into twobranches, one of which is directed to a low-pass filter having cutofffrequency of 20-kHz to extract the vital sign signal. The other branchcan pass through a 58-82-MHz bandpass filter, and the harmonics of80-MHz beat signal can be filtered out. Then the 80-MHz beat signalcorresponding to the first term of v₄(t) can be fed back to thephase-frequency detector, where it can be divided into 10-MHz anddiscriminated with the 10-MHz reference:

v ₅(t)=sin(2πf _(ref) t+ϕref)  (8)

where f_(ref) and φ_(ref) are the frequency and phase of the referenceoscillator, respectively. The phase frequency detector can discriminatethe phase difference of the beat signal and the reference signal andoutput an error signal. This signal can be filtered by the low-passfilter and then drive the VCO to produce an 80-MHz IF signal, with aphase that can be pre-adjusted to cancel the noise and achieve alow-noise 80-MHz beat signal. When the loop is locked, the phaserelationship between v₅(t) and the first term of v₄(t) may be:

[2π(f _(a) +f _(v))t+φ _(n)]+φ_(v)=8φ_(ref)  (9)

With (9), the beat signal v₄(t) can be rewritten as:

{tilde over (v)} ₄(t)=sin(2πf _(v) t+8φ_(ref))+sin[2π(f _(b) −f _(a) +f_(v))t+2π(f _(b) −f _(a))τ+(φ_(b)−φ_(a)+8φ_(ref))]  (10)

By phase-locking the 80-MHz beat signal to the 10-MHz reference signalprovided by the low-noise reference oscillator, the phase-locked loopcan control the VCO to pre-adjust its phase. Thus the phases of thetransmitted carriers can be adjusted for canceling the residual phasenoise and path noise. As a result, the phase noises of both the beatterms shown in {tilde over (v)}₄(t) can be suppressed to the level ofthe reference.

By passing the beat signals through the low-pass filter, the 80-MHz beatsignal can be filtered out, and the time domain vital sign signal can beobtained in the oscilloscope. Combined with f_(b)−f_(a)+f_(v)=0 andτ=τ_(x)+τ₀, the second term of {tilde over (v)}₄(t) represents the vitalsign signal.

$\begin{matrix}{{\nu_{7}(t)} = {\sin\left\{ \left\lbrack {{2{{\pi\left\lbrack {f_{b} - f_{a}} \right)}\left\lbrack {\frac{2d_{0}}{c} + \frac{2{x(t)}}{c}} \right\rceil}} + \left( {\varphi_{b} - \varphi_{a} + {8\varphi_{ref}}} \right)} \right\} \right.}} & (11)\end{matrix}$

Here, d₀ is constant and φ_(ref) is low noise in the system. As both the5.60- and 5.68-GHz signals are phase-locked to the 10-MHz reference,φ_(b)−φ_(a) has a noise level similar to that of 8φ_(ref). Therefore,the noise in v₇(t) is suppressed when the loop is locked, resulting inlow noise in the vital sign signal.

Frequency Domain Mathematical Analysis

For purposes of understanding the noise suppression mechanism, FIG. 2can be simplified to a linear frequency domain model, as shown in FIG.4. The noise and vital sign signals (τ_(x)) are contained in thefrequency downconverted signals φ₄ (s). After the band (BPF) andlow-pass (LPF) filtering, the beat signal (noise information) φ₆(s) andvital sign signal φ₇(s) can be obtained, where φ₆(s) and φ₇(s)correspond to carriers a and b, respectively:

φ₆(s)=[φ_(v)(s)+(φ_(a)(s)]e ^(−sτx)−φ_(a)(s)+φ_(n)(s)  (12)

φ₇(s)=φ₆(s)+[φ_(b)(s)−φ_(a)(s)]e ^(−sτx)  (13)

where φ_(a)(s)=Aφ₅(s), φ_(b)(s)=Bφ₅(s)), and A and B are the frequencyratios between their carriers and reference, respectively, as carrier aand b can be locked to the reference signal ϕ₅(s) at a phase-frequencydetector (K_(D)). As illustrated at FIG. 4, the feedback signal can alsobe locked to φ₅(s), and φ₆(s)=Nφ₅(s). Thus, the transfer functionbetween the vital sign signal and reference, H(s)=ϕ₇(s)/ϕ₅(s), can bewritten as

H(s)=N+(B−A)e ^(−sτx)  (14)

Therefore, the noise performance of the vital sign signal can bedetermined by that of the reference signal, and the path and residualphase noise can be suppressed using the phase-frequency detector,low-pass filter, and the VCO (K_(d), F(s), and K_(v)/S respectively).The vital sign can be extracted as shown in (14). The transfer functionof the noise can be very complex, but it can be seen in FIG. 4 thatφ_(n)(s) is the noise of the controlled oscillation system. In thephase-locked loop, the noise can be high frequency passed and can besuppressed in the low-frequency vital sign signal. Thus the noise andvital sign signal can be suppressed and extracted through carriers a andb, respectively.

Due to the very low frequency of the vital sign signal (τ_(x)), it mayprove hard to exhibit the performance of phase noise suppression throughthe spectrum of (14). The 80-MHz feedback beat signal φ₆(s), which isthe first term of (13), can be used to demonstrate the noise suppressionperformance as it has the same suppression ratio as the vital signsignal. Its phase noise spectrum measured with a spectrum analyzer(Agilent E4440A) is shown in FIG. 5. As a comparison, the phase noisespectra of the reference and the beat signal of an unlocked system arealso provided. The unlocked system can be a modified system in FIG. 2 byconnecting the RF port of phase-frequency detector (K_(D)) to VCO(K_(v)/S) output instead of the down-converted signal and disconnectingthe auxiliary feedback.

FIG. 5 shows that the 80-MHz beat signal of the locked system, which canbe a controlled oscillation system to the loop, has a suppressed phasenoise within the 10-kHz loop bandwidth and exhibits a noise level thatis about 12-dB lower than the unlocked case at the 10-Hz frequencyoffset. Up to 50-Hz frequency offset, it can be stabilized to thereference signal and has almost the same noise level. At a frequencyoffset of more than 10 kHz, which is the loop bandwidth, the noises arenot suppressed due to phase-locked loop's high-pass characteristics forthe controlled oscillation system's signal. This demonstrates that thephase-locked loop can successfully suppresses the residual phase noiseand path noise, which facilitates detection of a clean vital signsignal.

Results

To verify that the systems described in accordance with FIGS. 2-5introduce no extra noise, the measurement result of the unlocked system,which is a modified design in FIG. 2 as mentioned before, was comparedwith that collected by a direct vital sign detection system shown inFIG. 6. In the direct measurement scheme, the PNA network analyzertransmits a microwave signal, receives and demodulates the reflectedsignal, and then displays a time domain vital sign signal. Thetransmitting power in port 1 of the network analyzer is approximately 6dBm, and the antenna is about 50 cm away from the human subject. A timedomain signal of 25 s was recorded and analyzed in the frequency domain,represented by black lines in FIG. 7a . With the same transmit power anddetection distance, the vital sign detected with the unlocked system isexhibited by gray lines in FIG. 7 a.

In the time domain, respiration may be obvious, but the heartbeat, whichis superimposed on the respiration signal, may, in some instances behard to recognize. Using fast Fourier transform, the vital sign signalcan be represented in the frequency domain as shown in FIG. 7b . Therespiration frequency through direct measurement scheme can be 0.41 Hz,and the unlocked case can have a respiration frequency of 0.38 Hz. Thefrequency difference may be due to the status of the subject, as theexperiments are not conducted at the same time. The heartbeat, which maynot be as obvious or strong as the respiration signal, has a frequencyof around 1.3 Hz. As shown in the inset of FIG. 7b , the amplitude andfrequency of heartbeat in the two schemes are almost the same. Giventhat the results of the vital sign measurements from the unlocked systemand the direct detection are similar, the additional system componentsin the described systems do not introduce obvious extra noise.

The unlocked system was compared with the phase-locked loop design shownin FIG. 2. With the same transmit power and detection distance as inFIGS. 7a and 7b , the vital sign measurement results from both thesystems are illustrated at FIGS. 8a and 8b . With the exception that thevital sign signals have slightly different frequencies, the respirationrate from the locked system was quite similar to that of the unlockedcase and their amplitudes are similar, which might be due to thecondition of the subject. When the loop is locked, uncorrelated phasenoise is suppressed. Thus, a clearer heartbeat was obtained, meaningthat there was less possibility of inaccuracy in detection.

To further explore the detection performance of the locked system, themeasurement distance was altered to 100, 150, 200, 250, and 300 cmwithout changing the transmit power. As shown in FIGS. 9a-9e , theresults of the locked system are represented by black lines, while thoseof the unlocked system by gray lines. The time domain signal exhibitsthe periodical fluctuation, which is the respiration with heartbeatsuperimposed on it. The respirations of both the locked and unlockedsystems were around 0.4 Hz and even overlapping in FIG. 9b . For theheartbeat, the locked system has a clear frequency component at about1.2 Hz, which slightly changes at different detecting distances. As themeasurement of the unlocked system was conducted at a different time,the heartbeat frequency detected was around 1.0 Hz.

FIGS. 9a-9e shows that the heartbeat can be detected by the unlockedsystem at a distance of 100 cm, but it was hard to recognize when thedistance exceeds 150 cm. However, the locked system can still detect theheartbeat at 250 cm. At 300 cm, a quite rare wave is reflected back tothe loop; therefore, the heartbeat was severely noise-influenced andhard to detect. As respiration has a much larger displacement thanheartbeat, both the systems can still detect it at 300 cm.

Vital sign detection in four physical orientations was also conductedwith the same experimental setup as that in FIGS. 8a and 8b . During thedetection, the subject changes the orientation to let the antenna facethe front, back, left, and right sides of the subject. The measurementresults for the four orientations are shown in FIG. 10-10 d. Respirationcan be easily detected in all the four orientations. For the heartbeatsignal, it can be detected obviously when facing front and left (FIGS.10a and 10c ). When the antenna faces the back and right sides of thesubject, the heartbeat signal is very weak (FIGS. 10b and 10d ) due tothe less effective reflective area. The back side signal as shown inFIG. 10b has the worst noise level.

Discussion

In accordance with various implementations as described above, adual-carrier vital sign detection system with a noise suppression schemebased on phase-locked loop was demonstrated to automatically reduce theresidual phase noise and path noise. Through the phase discriminationbetween one carrier's beat signal and the low-noise reference signal inthe phase-frequency detector, noise can be extracted and then suppressedin the phase-locked loop, providing a clean transmission path for theother carrier. Therefore, the vital sign signal contained in the phaseof the second carrier can be obtained with low noise. Experiments withlocked and unlocked system have been carried out to compare the noiseand detection performance. The results show that systems in accordancewith embodiments of the present disclosure, can effectively suppress theresidual phase noise and path noise, improving the SNR by about 12 dB at10-Hz frequency offset, and significantly increase the detectiondistance of the weak heartbeat signal. The successfully demonstrateddetection distance for heartbeat is at least 250 cm, more than doublethe distance of the unlocked system. In addition, experiments wereconducted to demonstrate effective measurements of vital sign in fourphysical orientations.

CONCLUSION

The specific configurations, choice of materials and the size and shapeof various elements can be varied according to particular designspecifications or constraints requiring a system or method constructedaccording to the principles of the disclosed technology. Such changesare intended to be embraced within the scope of the disclosedtechnology. The presently disclosed embodiments, therefore, areconsidered in all respects to be illustrative and not restrictive. Thepatentable scope of certain embodiments of the disclosed technology isindicated by the appended claims, rather than the foregoing description,and all changes that come within the meaning and range of equivalentsthereof are intended to be embraced therein.

What is claimed is:
 1. A method for non-contact signal detectioncomprising: generating a noise pre-cancelled signal;frequency-modulating a first carrier signal and a second carrier signalwith the noise pre-cancelled signal to generate frequency-modulatedfirst and second carrier signals; transmitting, to a subject through apropagation pathway, a transmission signal comprising thefrequency-modulated first and second carrier signals; and receiving,from the propagation pathway, the transmission signal, wherein thetransmission signal is phase-modulated with a vibratory signalassociated with the subject.
 2. The method of claim 1 further comprisinggenerating the first carrier signal and the second carrier signal;wherein the first carrier signal and the second carrier signal arephased-locked with a second reference signal.
 3. The method of claim 1further comprising: receiving, by a noise precancellation system, a beatsignal extracted from the phase-modulated transmission signal; andsuppressing a phase noise and a path noise of the beat signal byphase-locking the beat signal to a first reference signal to generatethe noise pre-cancelled signal.
 4. The method of claim 1 furthercomprising extracting, from the phase-modulated transmission signal,information associated with the vibratory signal of the subject, and abeat signal.
 5. A method for detecting movement associated with asubject, the method comprising: generating, by a carrier source, a firstcarrier signal in phase coherence with a second carrier signal; using anoise pre-cancellation system, i) suppressing a phase noise and a pathnoise of a beat signal by phase-locking the beat signal to a firstreference signal to stabilize the phase of the beat signal, and ii)transmitting the noise pre-cancelled signal; using a modulator incommunication with the noise pre-cancellation system and the carriersource, i) frequency-modulating the first carrier signal and the secondcarrier signal with the noise pre-cancelled signal and ii) transmittinga transmission signal; transmitting, to the subject through apropagation pathway, the transmission signal; receiving, through thepropagation pathway and from the subject, a reflected signal includingthe transmission signal phase-modulated with a vibratory signalassociated with movement of the subject; and using a demodulator incommunication with the carrier source and the noise pre-cancellationsystem, i) receiving the reflected signal and the second carrier signal,and ii) transmitting the beat signal to the noise pre-cancellationsystem.
 6. The method of claim 5, wherein the generating, by the carriersource, the first carrier signal in phase coherence with the secondcarrier signal comprises phase-locking the first carrier signal and thesecond carrier signal with a second reference signal.
 7. The method ofclaim 5, wherein the first reference signal is generated by a low noisereference oscillator.
 8. The method of claim 5, wherein the suppressingthe phase noise and the path noise of the beat signal by phase-lockingthe beat signal to a first reference signal comprises: using a phasefrequency detector, i) receiving the beat signal and the first referencesignal; and ii) transmitting a phase control signal; and using a voltagecontrolled oscillator, i) receiving the phase control signal; and ii)pre-cancelling the noise associated with the beat signal.
 9. The methodof claim 5, wherein when the transmission signal is transmitted over thepropagation pathway, the first carrier signal and the second carriersignal are phase-modulated with the vibratory signal associated withmovement of the subject.
 10. The method of claim 5 further comprisingproviding auxiliary feedback to the demodulator by transmitting thetransmission signal to a third branch, the third branch in communicationwith and between the modulator and the demodulator.
 11. The method ofclaim 5 further comprising extracting, from the reflected signal, i)information associated with the vibratory signal of the subject, and ii)the beat signal.
 12. The method of claim 5, wherein the vibratory signalis associated with a vital sign of the subject.
 13. The method of claim5, wherein the first reference signal is generated by a low noisereference oscillator.
 14. The method of claim 6, wherein the secondreference signal is generated by a reference oscillator.
 15. The methodof claim 8 further comprising a low-pass filter.
 16. The method of claim11, wherein the extracting, from the reflected signal, is performed bythe demodulator.
 17. A non-contact signal detection system comprising:an oscillation system configured to receive a first carrier signal and asecond carrier signal and wirelessly transmit the first and secondcarrier signals to a subject generating a vibratory signal; and areceiver configured to receive modified first and second carrier signalsfrom the oscillation system; wherein the modified first carrier signalcomprises the first carrier signal phase-modulated with the vibratorysignal of the subject.
 18. The non-contact signal detection system ofclaim 17 further comprising a carrier source configured to generate thefirst and second carrier signals; wherein the carrier source isphase-locked to a first reference signal to establish phase coherencebetween the first carrier signal and the second carrier signal.